Introduce a SchedulerHelper in content/child/scheduler

content/renderer/scheduler/task_queue_selector.h

-// Copyright 2014 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_SELECTOR_H_
-#define CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_SELECTOR_H_
-
-#include <vector>
-
-#include "base/basictypes.h"
-
-namespace base {
-class TaskQueue;
-namespace trace_event {
-class TracedValue;
-}  // namespace trace_event
-}  // namespace base
-
-namespace content {
-
-class TaskQueueSelector {
- public:
-  virtual ~TaskQueueSelector() {}
-
-  // Called once to register the work queues to be selected from. This function
-  // is called on the main thread.
-  virtual void RegisterWorkQueues(
-      const std::vector<const base::TaskQueue*>& work_queues) = 0;
-
-  // Called to choose the work queue from which the next task should be taken
-  // and run. Return true if |out_queue| indicates the queue to service or
-  // false to avoid running any task.
-  //
-  // This function is called on the main thread.
-  virtual bool SelectWorkQueueToService(size_t* out_queue_index) = 0;
-
-  // Serialize the selector state for tracing.
-  virtual void AsValueInto(base::trace_event::TracedValue* state) const = 0;
-};
-
-}  // namespace content
-
-#endif  // CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_SELECTOR_H_